The autonomous parvoviruses are small, single-stranded DNA-containing viruses capable of inducing fetal demise and teratogenic effects during pregnancy and of interfering with both normal tissue turnover and the development of neoplastic disease in their adult host. The proposed research is aimed at understanding the mechanisms underlying the tissue-tropism exhibited by these agents during pathogenesis. Recombinant DNA techniques will be used in combination with viral and somatic cell genetics to analyse, at the molecular level, developmentally regulated host factors essential for viral growth, and the viral components with which the host factors interact - the combination of which determines virus strain-dependent target cell specificity. Viral determinants responsible for lethal viral gene expression in particular differentiated cells will be mapped by constructing and characterizing recombinants between strains of minute virus of mice (MVM) which differ in their ability to grow productively in fibroblasts and T-lymphocytes. Mutations allowing each parental virus to grow in an otherwise restrictive host cell will be mapped and sequenced. Host cell variants selected for resistance to the virus will be further characterized and exploited in cDNA cloning experiments designed to isolate the developmentally regulated host factors essential for viral, but not cellular, replication. The viral non-structural proteins will be studied to discover the role of each in pathogenesis. The two genes will be functionally separated by mutagenesis, and expressed in target cells, in order to assess their effects on cellular physiology. Bacterial reporter genes will be cloned under the control of each viral promoter, in concert with putative viral control elements, and their expression monitored in transfected cells, in order to explore both intra-viral genetic control circuits and the mechanisms of developmentally regulated control of viral gene expression. These approaches will also be used to develop in vitro systems in which to study the replication and hematotropism of the human parvovirus B19.